BACKGROUND:Poison Mushrooms are generally wild but many were placed in question blocks by the Koopa Troop to try to fool Mario and Luigi. Luckily Poisonous Mushrooms can normally be distinguished from other kinds of mushrooms by their dark purple or blue colouring.
Poison Mushrooms are just as dangerous as any monster and can not be destroyed by most normal means. In spite of their versatility they haven't been used often.

EVOLUTION:In their first appearance (Super Mario Bros. 2 Japan) Poison Mushrooms appeared in many different colours. They changed to the more common purple appearance with a skull on the cap in the Lost Levels version of the game.
Poison Mushrooms returned in Donkey Kong 94 where they looked like any old mushroom.
In Luigi's Mansion Poison Mushrooms appeared dark blue.
In the Super Smash Bros. adventures, Poison Mushrooms are are coloured a darker, more purple shade of red but otherwise look similar to regular Mushrooms.